Unlike many of you I don't think this was the right decision. Its not going to stop students from being wild this week, and I would bet people will still come into town this weekend. Cancelling veisha in the long run was a good idea, but this could cause the situation to escalate more. Now instead of rioting for no reason they may riot because it was cancelled.
Up the police presence and let nothing slide for the rest of the week. A slew of arrests might nip any retaliation in the bud.
Personally, I think a reasonable response for the future, I'd say cancel it until all current students are gone. Then you can pick it up again when you've got a full campus that hasn't experienced it before. That might help dispel the culture that surrounds it, since you won't have older students passing on the tradition to younger ones.